104 JAMES G. HUGHES, JR. 
of pepsin in 0.2 per cent HCL (the concentration being 0.5 
gram of commercial pepsin to 100 ce. of 0.2 per cent aqueous 
HCL). The electroplaxes were then treated with the following 
stains: (1) Iron hematoxylin. The result was that all the rods 
and part of the nuclei, and less dense portions of the electroplax 
had been digested. (2) Mallory’s connective tissue stain was 
applied, the electroplaxes being stained according to the direc- 
tions given in the first part of the paper. The results were 
the same as with the iron hematoxylin, namely, the less dense 
portions of the electroplaxes and the rods had disappeared. 
The fact therefore that these rods were disgested in 3 minutes 
by a weak solution of pepsin discredits absolutely the hypoth- 
esis that the rods are composed of elastic connective tissue, 
for elastic fibers are digested only very slowly by pepsin, the 
time required being several hours; the control in this case being 
the same as that noted above—the ligamentum nuchae of a 
horse. 
Having shown that the rods are not composed of connect- 
ive tissue of any sort, the next most logical hypothesis was 
that they were of some form of keratin, chitin, or chondrin, 
and the following test was performed accordingly. 
Vertical sections of the electroplaxes of Astroscopus, after 
the paraffin had been removed, were put for 24 hours in a 72 
per cent solution of hydrochloric acid. The acid was then 
washed out and the sections stained with iron hematoxylin 
and then examined with the microscope. The rods could not 
be found, but hollow spaces corresponding to the shapes of the 
rods were found in the electric layer of the electroplax. Figure 
3, a drawing of a slide after treatment with hydrochioric acid, 
shows these spaces clearly. The spaces are seen to be a little 
wider and larger than the rods, showing that the rods must 
have swelled to a certain extent before being dissolved by the 
acid. This latter statement was also confirmed by treating the 
rods with the acid for only a short time, and then examining 
with the microscope; the result being that the rods had swelled 
to a considerable amount. The other elements of the electro- 
plax, nuclei, etc., in their general form remained intact. There- 
